Punjab Effluent Treatment Society for Tanneries (PETS)
The Challenge
Treating One of India's Most Complex Industrial Effluents at Cluster Scale
The Punjab Effluent Treatment Society for Tanneries (PETS) operates the Common Effluent Treatment Plant for the tannery cluster at Jalandhar's Leather Complex — one of North India's largest concentrations of leather processing units. Tanneries in the cluster undertake the full range of leather processing operations: raw hide washing, de-hairing using lime and sulphides, chrome tanning, and finishing. Each stage generates wastewater with a distinct and highly problematic chemical signature.
The combined tannery effluent reaching the CETP carried COD of 3,500–5,000 mg/L, total dissolved solids of 12,000–14,000 mg/L, total chromium of 200–450 mg/L, sulphides of 140–300 mg/L, and chlorides of 5,000–6,000 mg/L. This combination — extreme organic load, hazardous heavy metals, high sulphate content, and very high TDS — places tannery CETP design in a category of its own. The existing 1.5 MLD first module was insufficient for the growing cluster, and PETS required technology design for a 5 MLD second module, with an explicit objective of achieving Zero Liquid Discharge — no treated effluent to be discharged from the complex under any circumstances.
Key Issues:
- !Chromium (Cr³⁺) concentrations of 200–450 mg/L requiring chemical precipitation as a mandatory first stage — bypassing biological treatment entirely if not removed upstream
- !High sulphate content (1,600–2,500 mg/L) making conventional anaerobic (UASB) treatment unsuitable — sulphate inhibits methanogenesis and creates a need for sulphur recovery, significantly increasing capital and operating costs
- !TDS of 12,000–14,000 mg/L far exceeding what biological treatment can address — requiring reverse osmosis as a tertiary stage
- !ZLD mandate from PETS requiring a five-stage treatment architecture extending beyond standard CETP design to include RO, evaporation, and crystallisation
- !Centralised treatment for multiple independent tannery units — each with different production schedules and effluent quality — requiring robust equalisation and buffering capacity
- !Hazardous sludge management: chrome-contaminated primary sludge requires careful segregation and compliant disposal under Hazardous Waste Rules
The Solution
Five-Stage Integrated CETP — From Chromium Precipitation to Zero Liquid Discharge
Spans Envirotech's approach began with a structured technology selection — evaluating aerobic activated sludge (ASP) against anaerobic UASB treatment for the biological stage. Drawing on independent research by IIT Kanpur comparing the two processes in tannery CETPs at Jajmau (Kanpur) and Unnao, we recommended two-stage aerobic ASP over UASB. The IIT Kanpur study found that high sulphate concentration in tannery effluent requires dilution with domestic wastewater to make UASB viable — increasing reactor size, sludge production, and lifecycle cost — while also producing fully chromium-contaminated hazardous sludge throughout the entire sludge stream. ASP, by contrast, confines chrome contamination to primary sludge only and delivers a lower total annualised cost per cubic metre treated.
The proposed CETP design integrates five treatment stages in sequence. Physico-chemical primary treatment at elevated pH precipitates chromium and removes heavy suspended solids before the effluent enters biological treatment. The biological stage uses two-stage activated sludge — a high-rate first stage (bio-sorption mode) followed by a lower-rate polishing stage — in two parallel streams of 2.5 MLD each for operational resilience. Tertiary treatment via chlorination and pressure sand filtration brings the effluent to the quality required for reverse osmosis feed. The RO system recovers 70–75% of the feed as treated permeate suitable for reuse within the complex. The concentrated RO reject — carrying the remaining TDS burden — is directed to a Multiple Effect Evaporator and crystalliser that recovers condensate and separates dissolved salts as a recoverable solid, completing the ZLD circuit.
Technologies Deployed:
Implementation Timeline:
Phase 1: Technology Assessment & Process Selection
Evaluated aerobic versus anaerobic biological treatment alternatives against IIT Kanpur comparative CETP data. Confirmed two-stage ASP as the optimum technology based on lifecycle cost, sludge management, and compliance reliability. Developed design basis for all five treatment stages.
Phase 2: Preliminary Engineering & Cost Estimation
Prepared process flow schematics, equipment sizing, and civil layout for all treatment stages — from screening through to the ZLD MEE-crystalliser circuit. Developed stage-by-stage capital cost and operating cost estimates to support PETS's investment planning.
Phase 3: Detailed Design & Procurement Support
Produced detailed engineering drawings, specifications, and equipment tender documents. All wetted components specified in corrosion-resistant materials — RCC with epoxy lining for civil structures, SS 304 for agitators and mixers, and Incoloy/Hastelloy for MEE heat transfer surfaces handling high-TDS concentrate.
Phase 4: Commissioning & Process Optimisation
Supervised installation and commissioning of the integrated treatment train. Optimised chemical dosing for chromium precipitation and biological process startup. Fine-tuned RO operating parameters and ZLD circuit performance to achieve PETS's zero-discharge objective.
The Results
Engineering Depth Across Five Treatment Stages
5 MLD
Design Capacity
Second-module CETP expanding the Jalandhar Leather Complex's treatment capacity — one of the largest centralised tannery effluent treatment systems designed in North India
5 Stages
Treatment Architecture
Fully integrated treatment train from physico-chemical chrome removal through biological treatment, tertiary polishing, reverse osmosis, and ZLD evaporation — designed as a single coherent system
Evidence-Led
Technology Selection
ASP recommended over UASB based on IIT Kanpur comparative CETP research — accounting for sulphate inhibition, chrome-contaminated sludge management, and total annualised cost per m³ treated
70–75%
Water Recovery Design
RO system engineered to recover 70–75% of tertiary-treated effluent as clean permeate for reuse within the complex — directly reducing cluster-wide freshwater demand
Integrated
ZLD Pathway
Complete zero-discharge architecture designed — RO permeate for process reuse, MEE-crystalliser circuit for TDS-rich reject, with solid salt recovery as the terminal output
MoEF + PPCB
Compliance Basis
Treatment scheme designed to meet all Ministry of Environment and Forests Schedule VI standards and Punjab Pollution Control Board norms for tannery effluent discharge
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